Surgeries at the human eye lens belong to the surgeries most commonly carried out in the world. Such surgeries become necessary due to pathologic processes which in most cases concern the interior of the eye lens, for example a turbidity of the eye lens (cataract formation) and/or a hardening of the lens core in case of presbyopia. In modern surgery methods, the interior of the eye lens (nucleus, cortex) is removed. For this, the lens capsular bag is preferably only opened from the front and the rest is left as it is. The capsular bag, which is empty after the interior of the natural eye lens has been removed, then generally serves to receive an artificial intraocular lens (IOL) which replaces the removed inner parts of the eye lens and reconstitutes the eyesight of the patient taking into consideration the desired optical correction of the eye.
Modern intraocular lenses may be produced individually for the patient concerned and, for this purpose, have most diverse optical properties with respect to asphericity, multifocality, toric surfaces and the like, to cope with and correct the diverse causes of (natural) ametropia of the patient concerned. For these inherent features of the individually produced lens to perform their function as correctly as possible, a preferably optimal centering of the lens and its association with certain reference systems in the optical system of the eye are strived for. So, the intraocular lens should be in general reliably placed concentrically to the pupil center, taking into consideration the visual line and the center of the entrance pupil, in particular in the capsular bag, but also in the sulcus ciliaris or the anterior chamber of the eye, where especially with toric intraocular lenses or phakic toric IOLs (IOLs which are implanted in addition to one's own lens), an axially accurate positioning is also important. Here, in case of malrotation, the predicted refraction target will deviate from the actually achieved target all the more the greater the rotation and the refractive power of the cylinder portion of the implanted lens are. However, not only the correct orientation in the X- and Y-axis of the optical system of the eye matters, but a preferably permanent and accurate positioning of the lens in the Z-direction (along the optical axis) without any tilting of the IOL is also desired.
While there are measuring and projection systems which may indicate the corresponding refraction and the resulting axes, or via certain reference points the axes in the eye, to the surgeon during surgery, these optical determination systems calculate the power of the IOL from the total refractive power of the eye.
However, a direct measurement of the optical power and position of the lens via their radii of curvature is desirable. Especially if an astigmatism of the eye, which often emanates from the cornea (so-called irregular curvature of the cornea), is to be corrected with an IOL, one has to see that the axis of the corneal astigmatism to be corrected exactly corresponds to the cylinder axis of the toric IOL. Already with a minor malrotation of the IOL axis, major errors in the complete imaging system of the eye are likely to occur; e.g. a malrotation of about 15° of an IOL already results in a loss of 50% of the cylinder correction and a considerable axial rotation of the remaining total error in the optical system.
In toric IOLs, the axis of the cylinder effect is normally indicated by manufacturer′ markers on the lens system. These, however, have a certain error tolerance of normally 3° which may lead to corresponding total errors in the refraction of the eye (see above).
Ophtalmologic apparatuses and methods for checking the optical properties of an eye with or without artificial lens are known, for example, from DE 10 2008 034 490 A1, DE 10 2005 042 436 A1, DE 10 2005 031 496 A1, DE 295 17 578 U1, DE 198 17 047 A1, JP 01308552A, CH 699 886 A1, WO 2011/030509 A1, CA 1099965, or DE 26 43 344 A1. It turned out, however, that said apparatuses are either complicate to handle or are not suited for reliably determining the orientation of an artificial lens in an eye.